PURPOSE OF SONG 139 



the air whilst uttering its plaintive wail ; the 

 cock Grouse, as if dissatisfied with its " crowing," 

 springs into the air and becomes a conspicuous 

 object of the moor ; the wary Redshank, poised 

 on flickering wings, forgets its mournful alarm 

 cry, and finds again its melodious song ; and 

 even the secretive Grasshopper- Warbler crawls 

 out of the midst of the thicket in order to " reel," 

 just as, for a similar reason, Savi's Warbler 

 climbs to the top of a tall reed. In fact the 

 males of most species, when they are finally 

 established on the breeding grounds, make 

 themselves as conspicuous as possible by sight 

 and by sound. And since the sounds produced 

 by no two species are exactly alike, the females 

 are able to recognise their prospective mates, 

 and the males that are still in search of ground 

 have ample warning if that upon which they are 

 treading is already occupied. So that you see, 

 from the remarkable development of the vocal 

 powers in the male, there follow two important 

 results — " recognition " and " warning." 



We here turn from song as the expression of 

 an instinctive disposition, and the question of 

 what calls forth this expression, to the impression 

 produced by the song on the hearer. 



Most birds have a call-note or a number of 

 call-notes, which, generally speaking, are specifi- 

 cally distinct. But to the human ear they are not 

 always so, perhaps because our power of hearing 

 is less sensitive than that of a bird, and unable to 

 appreciate delicate differences of tone. Be this 

 as it may, however, the fact remains that we 



